1. Field of the Invention
The present invention relates to a manufacturing method of an absorbent article including a front waistband region, a rear waistband region, and a crotch region located between the front waistband region and the rear waistband region.
2. Description of the Related Art
An absorbent article, such as a disposable diaper, includes a front waistband region, a rear waistband region facing the front waistband region, and a crotch region located between the front waistband region and the rear waistband region.
A manufacturing method of such an absorbent article includes a step of bonding a continuum of the front waistband region and a continuum of the rear waistband region in predetermined regions each corresponding to a bonded region of the front waistband region and the rear waistband region after overlapping the continuum of the front waistband region and the continuum of the rear waistband region under conveyance (hereinafter, referred to as bonding step).
Conventionally, an ultrasonic bonding device has been used in the bonding step. The ultrasonic bonding device includes; an anvil roll which supports the continuum of the front waistband region and the continuum of the rear waistband region while rotating in a conveyance direction; an ultrasonic horn which applies ultrasonic vibration to each predetermined region corresponding to the bonded region of the front waistband region and the rear waistband region while pressing the predetermined region against the anvil roll; and an ultrasonic vibrator which supplies the ultrasonic vibration to the ultrasonic horn.
In order to reliably bond the continuum of the front waistband region and the continuum of the rear waistband region, the ultrasonic horn is formed to be longer than a length of the bonded region, in a direction (hereinafter, referred to as Crossing Direction (CD)) perpendicular to a conveyance direction (hereinafter, Machine Direction (MD)), of the continuum of the front waistband region and the continuum of the rear waistband region.
There is known a method of monitoring a bonded state of the continuum of the front waistband region and the continuum of the rear waistband region after such a bonding step (for example, see Japanese Patent Application Publication No. H 6-341966 (pages 2 and 3, FIGS. 1-3)). This method makes it possible to detect whether or not a failure (abnormality) has occurred in the bonded state in the bonded region by measuring a current which flows into the ultrasonic vibrator.
Meanwhile, when the ultrasonic horn presses the predetermined region against the anvil roll, the ultrasonic horn may incline with respect to the anvil roll, and thus the ultrasonic horn may become unable to press one end side in the CD of the predetermined region.
However, by the conventional method described above, even if the ultrasonic horn has inclined with respect to the anvil roll, it is determined that no failure occurs in the bonded state as long as the current satisfies a specified condition, since only the current is measured.
Therefore, the conventional method has a problem that a failure occurred in the bonded state cannot be detected in such a case. In particular, if the failure occurs in the bonded state in a disposable diaper, the disposable diaper cannot take form as a product of an underpants-type diaper; for it allows separation of a bonded region while in use, for example.
Accordingly, an object of the present invention is to provide a manufacturing method of an absorbent article capable of reliably detecting whether or not a failure has occurred in a bonded state of a predetermined region corresponding to a bonded region of a front waistband region and a rear waistband region.